Method of making metal foam



United States Patent 3,379,517 METHQD (BF MAKING METAL FOAM Leslie G. Graper, Dailas, Tern, assignor to LOR Corporation, Enid, (Tilda, a corporation of Delaware No Drawing. Filed Oct. 23, 1965, Ser. No. 504,132 3 Claims. (Cl. 75-20) ABSTRACT OF THE DISCLQSURE An improvement in making a metal foam body is pro-' vided which involves adding a particulate solid oxidizing agent, of which a preferred example is MnO to the molten mixture from Which the foam is made.

This invention relates to a method of making metal foam.

Patent application Ser. No. 264,438, filed Mar. 11, 1963, soon to issue as Patent 3,214,265, relates to the subject matter hereof.

It has been known heretofore to produce metal foam defined in previous patents issued to the Same assignee and in the aforementioned patent application by mixing with a molten metal such as aluminum, zinc, lead and the like or alloys thereof, a foaming agent especially a metal hydride, such as titanium hydride, magnesium hydride, lithium aluminum hydride or the like.

It has heretofore been believed that the hydride after being mixed into the molten metal decomposed entirely as a result of the heat introduced thereinto from the molten metal to provide titanium, zirconium, magnesium or the like and hydrogen gas, which gas provided the closed cells or bubbles in the metal foam body produced by the process.

It has been discovered that although this action takes place it is not the primary action which takes place, and that the primary action which takes place is represented by the following exemplary equation given for titanium hydride:

2 %Og EiHz TiO T The aforementioned application discloses adding air, oxygen, superheated steam and the like to molten metal in order to effect foaming thereof.

Furthermore, in the process described in said application and in previous applications which have described the use of metal hydrides as foaming agents to produce metal foam, air has been stirred into the mixture of foaming agent and molten metal merely because the process has been operated in ambient atmosphere and not in an oxygen-free atmosphere.

It has now been found that if air or oxygen is excluded, substantially no foaming is obtained and it has been thus demonstrated that one of the processes which actually occurred in such previous process was the reaction of the hydride with oxygen obtained from the air or from oxygen or from steam to produce a metal oxide and release hydrogen.

In accordance with the present invention this discovery has been utilized to facilitate making foam with much reduced amounts of hydrides whereby the cost of producing metal foam has been materially reduced. By the addition of a suitable oxidizing agent such as manganese 3,379,517 Patented Apr. 23, 1968 dioxide, appreciable reductions in the amount of hydride which must be used can be accomplished.

In place of manganese dioxide there may be added pyrolucite which is an ore of MnO By adding such an oxidizing agent, metal oxide nuclei for the formation of cells are provided in superior manner. Thus, when MnO is added, particles of A1 0 are formed in accordance with the following equation:

which serve as nuclei for the formation of cells or bubbles.

Likewise, the metal oxide formed by the reaction of oxygen with the metal hydride, for example, TiO as set forth in the equation above also serve as such nuclei.

It is therefore an object of the invention to achieve the advantages realized by adding to the mixture of metal hydride and molten metal used to produce a metal foam body, a substance for supplying oxygen in amounts greater than heretofore available and in amounts which can be suitably controlled.

This object is accomplished by adding air, oxygen, steam or superheated steam or any one of many oxidizing agents, molten metal and metal hydrides, such additives normally being added at the same time the hydride is added to the molten metal.

One of the advantages thereby achieved is to greatly reduce the amount of hydride required whereby the cost of producing metal foam is very substantially reduced.

Another advantage is the provision of cell nuclei of metal oxide particles which results in the provision of foam having greater uniformity of cell size, cell distribution and cell shape.

Another advantage is that the criticality 0f temperatures at which molten metal is maintained prior to addition of metal hydride and additive in accordance with the instant case and the criticality of temperatures at which the mixture, after being thoroughly mixed, is poured and the criticality of temperatures at which molds are maintained are all reduced.

As one example, about 8 ounces of metal hydride were being used to provide adequate foaming for a preselected amount of aluminum-magnesium alloy to provide a suitable panel of metal foam. By addition of a small amount of MnO it was found possible to reduce the amount of hydride from 8 ounces to 1 ounce.

As another example it was found possible to produce a panel of an alloy of 13% (nominal) silicon, balance aluminum, which had excellent cell shape, cell uniformity and cell distribution and which had a density of 30 pounds per cubic foot and a compressive strength of greater than 2500 p.s.i., with a relatively small amount of MnO and a very low proportion of metal hydride. Such strength is substantially greater than it has been possible to produce as a matter of course heretofore.

It may thus be seen that the invention is broad in scope and includes such modifications as will be apparent to those skilled in the art and is to be limited only by the claims.

Having thus described the invention, it is claimed as follows:

1. The method of making a metal foam body which comprises mixing into a body of molten metal a small proportion of a metal hydride and a small proportion of a particulate solid oxidizing agent which provides oxygen for reaction with the metal hydride, intensively mixing the resulting mixture to provide an intimate mixture f the component, maintaining a suitable temperature to provide for reaction of the said oxygen with the metal hydride to thereby cause foaming of the molten metal by providing closed hydrogen containing cells therewithin and then cooling the resulting body.

2. The method of claim 1 wherein said oxidizing agent is MnO 3. The method of claim 1 wherein said oxidizing agent is pyrolucite.

References Cited UNITED STATES PATENTS 3,214,265 10/1965 Fiedler 7520 3,297,431 1/1967 Ridgway 7520 3,300,296 1/1967 Hardy et a1. 75--20 BENJAMIN HENKIN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,379 ,517 April 23 1968 Leslie G. Graper It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1 line 42 the formula should appear as shown below:

Signed and sealed this 23rd day of September 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Dfficer WILLIAM E. SCHUYLER, JR. 

